Whatever merit alternatives have, the reality is these make long, like very long migration arcs, these days you will have so much team churn, maintenance rabit holes and regular tech debt and feature requests that its fair enough to say any project that starts to move out of Mainframe tech will never see the finishing line.

You are better off maintaining what already works. Either way why do you want to migrate when things are just working fine as is?

And a lot of that COBOL will still be managed with ISPF over 3270 terminal connections.